Continuous casing of ferrous-based alloys is hindered by inclusion build-up and concentration in the upper nozzle, leading to clogging of the nozzle and resultant shut-down of the operation to clean the nozzle. Furthermore, the presence of inclusions in the cast material results in a lower quality cast material and in some cases even requires the cast material to be rejected. Therefore, molten ferrous-based alloy has been treated to hinder inclusion build-up or to remove inclusions, before, during, or after passing from the ladle to the tundish and on to the mold.
Presently used methods of inclusion removal are numerous. One approach is to provide the tundish with dams and wiers to give "dead spots" and differing flow characteristics, so as to allow the lighter inclusions to agglomerate and float to the surface. This approach is not sufficiently effective. Another approach is the use of porous plugs in the tundish, through which argon gas is bubbled, but this approach is also not adequate. Other approaches have built into the tundish "mazes", "picket fences" and other flow regulators and non-removable filters. Bed filtration of a molten alloy is illustrated by U.S. Pat. No. 4,330,327 to Pryor.
A further approach is to add mold powders to the mold so as to dissolve inclusions, but the resulting mass is not always removed from the alloy before it solidifies. Electromagnetic stirring and braking are also used to disperse or float out the inclusions in the mold, with mixed results.
The absence of efficient inclusion removal prior to the molten alloy passing into the upper nozzle has required the use of procedures to avoid clogging. For example, argon gas is bubbled through a porous upper nozzle, through porous plates on the slide gate, or through porous inserts in the submerged entry nozzle, to decrease, but not eliminate, inclusion build-up and eventual clogging.
Accordingly, there is a long-felt need for an improved apparatus useful in the continuous casting of ferrous-based alloys, for removing inclusions from the molten alloy. Such an improved apparatus would be especially useful if it removed inclusions prior to passage of the molten alloy into the upper nozzle. Moreover, such an improved apparatus would provide an even greater contribution to the art if it were based upon an inclusion-removing element that could be easily installed and removed, and hence could be replaced with minimal disruption of the continuous casting process. Clearly, such an apparatus would make possible an improved process for the continuous casting of ferrous-based alloys.